You will want to use 1.5 large dog tabs. They say 1 large tab is enough for about 300-350 gallons of water.
I never changed my water during the whole treatment.
Shut carbon off, uv off, skimmer off for first 24 hours.
I like to do treatment each week for minimum of 3 weeks, but prefer 4 weeks.
Remove shrimp and crabs they will die. Snails seemed to be fine.